MicroRNAs or miRNAs are small noncoding RNAs which function by regulating target gene expression post-transcriptionally. The breadth of genetic regulatory effects potentially mediated by microRNAs and their central role in diverse cellular and developmental processes (Ambrose (2004) Nature 431 (7006):350-5; Bartel & Chen (2004) Nat. Rev. Genet. 5 (5):396-400; Miska (2005) Curr. Opin. Genet. Dev. 15 (5):563-8; Sevignani, et al. (2006) Mamm. Genome 17 (3):189-202) has led to the suggestion that aberrant expression of microRNA genes could contribute to human disease, including cancer (McManus (2003) Semin. Cancer Biol. 13 (4):253-8; Caldas & Brenton (2005) Nat. Med. 11 (7):712-4; Lu, et al. (2005) Nature 435 (7043):834-8; Croce & Calin (2005) Cell 122 (1):6-7). A substantial number of microRNA genes are located in genomic regions that are frequently amplified, deleted, or rearranged in cancer, providing further evidence of a role for microRNAs in cancer pathogenesis (Calin, et al. (2002) Proc. Natl. Acad. Sci. USA 99 (24):15524-9; Nairz, et al. (2006) Dev. Biol. 291 (2):314-24). Deregulated microRNA expression has been documented in diverse cancers including lymphoma (Tagawa & Seto (2005) Leukemia 19 (11):2013-6; He, et al. (2005) Nature 435 (7043):828-33; Costinean, et al. (2006) Proc. Natl. Acad. Sci. USA 103 (18):7024-9; Kluiver, et al. (2006) Genes Chromosomes Cancer 45 (2):147-53 11-14), colorectal cancer (Michael, et al. (2003) Mol. Cancer. Res. 1 (12):882-91), lung cancer (Hayashita, et al. (2005) Cancer Res. 65 (21):9628-32), breast cancer (Iorio, et al. (2005) Cancer Res. 65 (16):7065-70), and glioblastoma (Ciafre, et al. (2005) Biochem. Biophys. Res. Commun. 334 (4):1351-8; Chan, et al. (2005) Cancer Res. 65 (14):6029-33). Specific microRNAs have been shown to target genes critical for the development of cancer such as E2F (O'Donnell, et al. (2005) Nature 435 (7043):839-43) and RAS (Johnson, et al. (2005) Cell 120 (5):635-47). In addition, Asangani, et al. ((2008) Oncogene 27:2128-2136) teach that microRNA-21 (miR-21) is involved in invasion, intravasation and metastasis in colorectal cancer and post-transcriptionally down-regulates tumor suppressor Pdcd4. Hence, microRNAs and the genes they regulate can potentially provide etiologic insights as well as serve as both diagnostic markers and therapeutic targets for many different tumor types.
Gliomas are tumors that occur in the central nervous system and demonstrate invasive growth. Glioblastomas in particular are the most resistant to treatment, and have an extremely poor five-year survival rate of about 8%. Although definitive efficacy of chemotherapy has only been confirmed for alkylating agents and temozolomide, their efficacy is limited to concomitant use with radiotherapy. On the other hand, post-surgical radiotherapy has been recognized to demonstrate life-prolonging effects. Knowledge of molecular biomarkers that are associated with genetic regulatory mechanisms contributing to malignancy is essential for elucidating the mechanisms underlying malignant transformation, for understanding pathologic attributes of Glioblastoma Multiforme (GBM), and ultimately for designing effective strategies for GBM treatment. MicroRNA-21 has been identified as a molecular biomarker of GBM (Gazer, et al. (2007) Cancer Res. 67:2456-68) and is correlated with glioma grade (Selcuklu, et al. (2009) Biochem. Soc. Trans. 37 (Pt 4):918-925; Krichevsky & Gabriely (2009) J. Cell Mol. Med. 13 (1):39-53; Gabriely, et al. (2008) Mol. Cell. Biol. 28 (17):5369-5380; Chan, et al. (2005) supra; Corsten, et al. (2007) Cancer Res. 67 (19):8994-9000; Papagiannakopoulos, et al. (2008) Cancer Res. 68 (19):8164-8172). Low levels of mir-21 are expressed in Grade II and Grade III gliomas, while significantly higher levels are observed in GBM (Gabriely, et al. (2008) supra; Papagiannakopoulos, et al. (2008) supra). Chan, et al. ((2005) supra) also teach that levels of miR-21 are markedly elevated in human glioblastoma tumor tissues, early-passage glioblastoma cultures, and in six established glioblastoma cell lines, wherein knockdown of miR-21 in cultured glioblastoma cells triggers activation of caspases and leads to increased apoptotic cell death. Moreover, Papagiannakopoulos, et al. ((2008) supra) and Gabriely, et al. ((2008) supra) teach that down-regulation of miR-21 in glioblastoma cells causes repression of growth, increased apoptosis, and cell cycle arrest.
Pdcd4 (Programmed Cell Death 4), a known tumor suppressor gene, has been identified as a functional target of mir-21 (Lu, et al. (2008) Oncogene 27 (31):4373-4379; Zhu, et al. (2008) Cell Res. 18 (3):350-359) and has been shown to regulated by mir-21 in GBM (Chen, et al. (2008) Cancer Lett. 272 (2):197-205). However, the effect of mir-21 regulation of Pdcd4 on specific biological activities of pathologic potential such as apoptosis, proliferation, anchorage-independent growth, or more significantly in vivo growth of GBM xenografts has not been previously examined.